Firefox doesn't handle the CSV format for logins / password data. The old Legacy version of Firefox (Fx56 Australis and earlier versions) did have some 3rd party add-ons available which would export and import via CSV, but the Quantum versions don't support the defunct Legacy format extensions.

Firefox doesn't handle the CSV format for logins / password data. The old Legacy version of Firefox ''(Fx56 Australis and earlier versions)'' did have some 3rd party add-ons available which would export and import via CSV, but the Quantum versions don't support the defunct Legacy format extensions.

So what's missing from this equation is the code to read your CSV file, extract out the fields for each login, and assemble them into the correct format to add to Firefox.

It's probably possible to write a script that adds passwords from a CSV file, but if you don't find one online, it's going to take some work.
First, because legacy extensions no longer run, you will need to execute a "legacy" script in the Browser Console. To do that, you need to turn on "chrome debugging" as follows:
(1) In a new tab, type or paste '''about:config''' in the address bar and press Enter/Return. Click the button promising to be careful or accepting the risk.
(2) In the search box above the list, type or paste '''devt''' and pause while the list is filtered
(3) Double-click the '''devtools.chrome.enabled''' preference to switch the value from false to true
And then you may need more information about the Browser Console: https://developer.mozilla.org/docs/Tools/Browser_Console
This is a script that adds a single saved login:
<pre>/*
Sequence of fields for init():
login.hostname, login.formSubmitURL, login.httpRealm,
login.username, login.password, login.usernameField, login.passwordField
*/
try {
var loginInfo = Components.classes["@mozilla.org/login-manager/loginInfo;1"].createInstance(Components.interfaces.nsILoginInfo);
// Create the new login info object
loginInfo.init("https://www.jeffersonscher.com", "https://www.jeffersonscher.com/res/logintest.html", null,
"me", "secret123", "uname", "pass");
// Add the new login to Firefox's password manager
Services.logins.addLogin(loginInfo);
} catch (err) {
console.log('Problem adding login: '+err);
}
</pre>
Then that should show up in the Saved Logins dialog, and it may or may not auto-populate on the test page https://www.jeffersonscher.com/res/logintest.html (I got flaky results).
So what's missing from this equation is the code to read your CSV file, extract out the fields for each login, and assemble them into the correct format to add to Firefox.